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This becomes active during the early stages of infection. Defences include:
 
This becomes active during the early stages of infection. Defences include:
 
*Interferon (IFN)- typically stimulates the inhibition of viral replication. There are three known types:
 
*Interferon (IFN)- typically stimulates the inhibition of viral replication. There are three known types:
**Infection of a cell by a virus stimulates production of IFN-alpha and IFN-beta, which activate genes in neighbouring cells. One of these genes, for example, codes for a protein kinase that blocks translation of proteins. Another activates an endonuclease that degrades viral RNA.  
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**Infection of a cell by a virus stimulates production of IFN-α and IFN-β, which activate genes in neighbouring cells. One of these genes, for example, codes for a protein kinase that blocks translation of proteins. Another activates an endonuclease that degrades viral RNA.  
 
**IFN-γ increases the expression of MHC I and II, enhancing the function of the adaptive immune response. It also activates macrophages and NK cells.
 
**IFN-γ increases the expression of MHC I and II, enhancing the function of the adaptive immune response. It also activates macrophages and NK cells.
 
*Natural killer (NK) cells- one of the main mediators of antibody-dependent cell-mediated cytotoxicity
 
*Natural killer (NK) cells- one of the main mediators of antibody-dependent cell-mediated cytotoxicity
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